1. Field of the Invention
The invention relates to periscopes for observing an exterior field of view from within a protected structure, and particularly to a periscope for armored vehicles. More particularly, the invention relates to a periscope having internal ballistic protection preventing transmission of shock waves encountered by the exterior portion of the periscope from being transmitted through the periscope and propelling fractured pieces of the periscope into the interior of the vehicle.
2. Description of the Prior Art
Numerous periscope constructions have been developed and are in use for armored vehicles such as tanks. These periscopes contain various optical systems which enable the occupants to observe a field of view exterior of the vehicle without providing a direct opening through the armor for passage of projectiles, chemicals, liquids or other harmful materials. Many periscope constructions presently used on tanks consist of a single block of clear plastic mounted within a protective housing which extends through an opening in the tank. The observer views an exterior field of view through window openings in diagonally opposite end portions of the block.
Even though the body of a periscope which provides the optical system is formed of solid plastic, it still exhibits ballistic problems. When a projectile strikes the exterior viewing window of the periscope a shock wave is transmitted through the body and causes parts and pieces of the observer window and surrounding plastic body to fly out into the interior of the vehicle and strike the observer and tank occupants. All known periscopes having solid bodies forming the optical system exhibit this problem to one degree or another.
One known approach for solving this shock wave transmission problem is to split the transparent periscope body into two sections and fill the void or space therebetween with an inert gas such as dry nitrogen to prevent the accumulation of moisture, condensation and dust. This gas filled space prevents transmission of shock waves therethrough, but requires an airtight seal formed by gaskets and adhesives which is a weak point in the periscope construction. The seal often fails because of the harsh environment to which the periscope is subjected, as well as adding considerable cost to the periscope. Periscopes such as shown in U.S. Pat. Nos. 2,361,050, 3,482,897, 3,551,020 and 3,619,040 attempt to solve this shock wave transmission problem by such gas filled voids.
The periscope construction shown in my copending application, Ser. No. 697,933, filed June 21, 1976, now U.S. Pat. No. 4,065,206 eliminates many of the problems and shortcomings of these known prior periscopes. The periscope of this invention provides a completely different approach than that of my previous construction and is believed to achieve the desired results.
No other periscope construction of which I am aware eliminates these problems in a simple, effective and inexpensive manner by formation of the optical transparent block of the periscope into a pair of sections which are separated by a transparent hollow cell filled with an inert gas or with a vacuum being formed therein to reduce the transmission of shock waves between the two sections.